Bead for a tire having extended mobility

ABSTRACT

A tire for a vehicle wheel, comprising two sidewalls, a crown zone provided on its radially outer portion with a circumferential tread, and a bead arranged in the radially inner portion of each of the sidewalls. Each bead comprises a seat and an outer flange which are intended to come into contact with the rim, the seat having a generatrix, the axially inner end of which lies on a circle of diameter greater than the diameter of the circle on which the axially outer end is located. A carcass-type reinforcement structure extends substantially radially from each of the beads, along the sidewalls, towards the crown zone. Each bead includes a zone for anchoring the carcass-type reinforcement structure in the bead, a bearing zone for the bead against a suitable rim seat, and an intermediate zone, which is provided substantially between said anchoring zone and the bearing zone.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of international application PCT/EP00/12061 filedNov. 30, 2000, which was published in French on Jun. 7, 2001 asinternational publication WO 01/40000 A1, and which claims priority toFrench application 99/15367 filed Dec. 3, 1999.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The present invention relates to a tire for a vehicle wheel in which atleast one of the beads comprises a seat having a generatrix, the axiallyinner end of which lies on a circle of a diameter greater than thediameter of the circle on which the axially outer end is located. Thistype of design is particularly suited to the new generations of tireswhich can be used, within certain limits, in conditions of low pressure,or even zero or virtually zero pressure, with the risk of separation ofthe tire from the rim on which it is mounted being eliminated. Thisconcept is frequently designated by the expression “extended mobility”.

2. The Related Art

For a long time, tire manufacturers have been trying to develop a tirewhich does not create any source of potential risk or danger in theevent of an abnormal drop in, or even total loss of, inflation pressure.One of the difficulties encountered relates to travelling with a flattire or at very low pressure. In fact, when travelling at very lowpressure, or even at zero pressure, with conventional tires, the beadsare at great risk of separating from the periphery of the rim againstwhich they are held by the inflation pressure.

Numerous solutions have been tested in order to overcome thesedisadvantages. Frequently, these solutions cause additional difficultiesin mounting/demounting the tire on/from the rim.

EP 0 582 196 (U.S. Pat. No. 5,660,656) discloses a tire comprising atread extended by two sidewalls and two beads and also a carcassanchored in the two beads to an annular reinforcement. The carcass isformed of cords in an adjacent arrangement, which are alignedcircumferentially and are in contact with at least one layer of bondingrubber of very high elasticity modulus in the hooking zone of the beadcomprising the annular reinforcement. In this tire, the annularreinforcement of the hooking zone of the bead is formed of stacks ofcircumferential cords with the interposition of a layer of bondingrubber of very high elasticity modulus between the reinforcement cordsof the carcass and the stacks of circumferential cords.

This embodiment is intended for tires of conventional type, with thebeads being held against the rim hook due to the inflation pressure ofthe tire. In this type of arrangement, there is a predominance ofstresses of the lateral or axial type, which induces major compressiveforces that act substantially axially from the sidewalls towards thecenter of the bead. These forces increase according to the inflationpressure. The increase in pressure tends to make the bead slide againstthe hook, radially towards the outside. The stresses induced radiallytowards the inside, against the seat of the rim, decrease with anincrease in pressure, or with any increase in the tension of thecarcass-type reinforcement structure.

It will furthermore be noted that the stacks of cords are aligned in adirection substantially parallel to the orientation of the profile ofthe rim hook against which the bead bears.

The profile of the bead of this type of tire is relatively narrow andelongated; the anchoring is distributed over the major part of theheight and width of the bead. The passage of the carcass into the beadis generally substantially central relative to the walls of the bead.

Furthermore, when a relatively narrow bead is subjected to predominantlyaxial stresses, neither the inflation pressure nor the tension inducedin the carcass permits the generation of large moments or torques, whichtend to make the bead pivot or turn on itself.

With such a type of tire, if the pressure drops and the vehiclecontinues to travel, the holding of the tire on the rim is no longerensured, and in the majority of cases it rolls off the rim.

EP 0 673 324 (U.S. Pat. No. 5,634,993) describes a rolling assemblycomprising at least one tire with a radial carcass reinforcement whichis anchored within each bead and a rim of specific shaping. This rimcomprises a first seat, with a generatrix such that the axially outerend of the generatrix is spaced from the axis of rotation by a lengthless than the spacing between its axially inner end and the axis ofrotation, and is defined axially to the outside by a protrusion or rimflange. The tire comprises bead seats suitable for mounting on the rim.The type of tire/rim interface proposed in this document has manyadvantages compared with the solutions already known, in particular withregard to the ease of mounting/demounting, while making it possible totravel a certain distance despite a drop in pressure.

The present invention is directed in particular at proposing certaintypes of architecture in order to optimize the qualities of the assemblyproposed in the document referred to above.

EP 0 748 287 (U.S. Pat. No. 6,179,028) describes a solution whichpermits initial optimization of the basic technology described in EP 0673 324 referred to above. This is a tire, at least one bead of whichhas a structure that makes it possible to modify the clamping of thebead according to the tension of the carcass reinforcement and, inparticular, reinforcement thereof when the inflation pressure increasesto its rated value. The document thus proposes using a bead withanchoring of the end of the carcass by turning it up about the base ofthe bead wire, via the axially and radially inner sides relative to thebead wire. The bead also comprises, adjacent to the bead wire andaxially to the outside thereof, a profiled element of rubber mix ofrelatively high hardness against which the bead wire can exert acompressive force when the tension of the carcass reinforcementincreases. This compressive force creates self-clamping of the toe ofthe bead on the mounting rim. The tension of the carcass thereforeinvolves displacement of the bead wire towards the outside, so that thelatter generates the compressive force. In such a configuration, thepresence of a bead wire of conventional type and the turning-up of thecarcass beneath the latter are presented as being indispensable forgenerating the compressive force. This restricts the other types ofarrangement which can be considered

Moreover, EP 0 922 592 describes two embodiments with the carcassanchored by turning it up axially towards the outside. The firstembodiment proposes anchoring of the carcass in the bead by turning itup radially towards the outside of the end of the carcass. The upturn issurrounded on either side by two radially superposed layers of metalwires arranged axially side by side and covering substantially all ofthe axial portion along the seat of the bead. The layers are arranged soas to be parallel to the seat. The types of cords and the correspondingdimensions are very precise.

The second solution proposed in this document relates to bead seats withdifferent diameters. The securing of the carcass is also effecteddifferently from the first solution. First of all, the carcass issubdivided into two portions which are radially separated at the levelof the bead. Each portion is adjoined by a layer of cords which isarranged radially, each layer being arranged radially to the outsideagainst each of the carcass portions. The radially outer carcass portionand the layer of cords radially to the inside are separated by an insertof the type of elastomer of high hardness provided in the bead. Thisinsert axially lines the central portion of the bead and rises radiallytowards the outside and axially towards the inside, beyond the radiallimit of the presence of the metal wires.

The two examples of solutions of EP 0 922 592 have severaldisadvantages. Thus, the securing of the carcass proposed in thisdocument requires the presence of an upturn axially towards the outsideof the end portion of the carcass. Furthermore, the superposed layers ofcords are arranged radially close to the seat of the bead, for a goodpart at a radial position closer to the axis of rotation than the upperportion of the flange on which the bead bears. Unless highly extensiblecords are used, it is difficult to mount/demount the tire, due to theunfavourable radial position of the cords. It will also be noted thatthe stacks are oriented substantially parallel to the profile of theseat against which the bead bears.

According to the second solution, the carcass is subdivided into twoportions and an insert of high hardness is necessary to separate, on theone hand, the layers of cords and, on the other hand, the two carcassportions. However, the carcass is not anchored in the insert. The formof the insert described is limitative.

SUMMARY OF THE INVENTION

It is an object of the present invention to overcome the variousdisadvantages inherent in the solutions set forth above.

To do this, it provides a tire for a vehicle wheel, comprising:

-   -   two sidewalls spaced apart axially from each other, joined at        their radially outer portions by a crown zone provided on its        radially outer portion with a circumferential tread;    -   a bead, arranged radially to the inside of each of the        sidewalls, each bead comprising a seat and an outer flange which        are intended to come into contact with a suitable rim;    -   a reinforcement structure extending substantially radially from        each of the beads, along the sidewalls, towards the crown zone;    -   at least one of the beads comprising:    -   a bead seat comprising a generatrix, the axially inner end of        which lies on a circle of a diameter greater than the diameter        of the circle on which the axially outer end is located;    -   an anchoring zone for the reinforcement structure in the bead,        comprising a substantially radial arrangement of circumferential        cords, the anchoring zone being arranged in the substantially        radially inner portion of the bead;    -   an intermediate zone, arranged substantially axially externally        to the anchoring zone and comprising at least one portion which        is radially external relative to the radially innermost portion        of the anchoring zone;    -   a bearing zone for the bead which is able to lie directly or        indirectly against the suitable rim seat, and extending        substantially axially along the bead seat and comprising at        least one portion arranged substantially radially internally to        the intermediate zone; and    -   the intermediate zone comprising a structure which permits the        transfer of forces from the anchoring zone to the bearing zone        of the bead so as to increase the bearing force of the seat of        the bead in its axially outer portion when a substantially        radially external tensile force is exerted on the reinforcement        structure at least at the level of the bead.

Such a configuration permits optimum holding of the bead on the rim, inparticular at the level of the rim seat/bead seat interface. The forcesacting on the anchoring zone are then transmitted effectively to thezone of the seat of the bead. The radial continuity makes it possible tominimize the impact of the shearing forces acting against the bead inits entirety.

The anchoring zone does not comprise a bead wire, in particular a beadwire of conventional type, such as, for example, a multi-cord bead wireagainst which a carcass ply is turned up, this bearing or contact orcooperation effecting the holding of the carcass.

Each of the zones taken in isolation, and also all the zones together,to some extent forms an internal bead capable of effecting relativemovements, such as, for example, of the angular or rotational type,relative to another zone, or relative to a virtual center of pressureCP, or relative to the seat of the rim, etc.

Advantageously, the intermediate zone ensures a mechanical connectionbetween the anchoring zone and the bearing zone. The intermediate zoneensures continuity between the other two zones, such that the mechanicalforces are transmitted from the anchoring zone towards the bearing zone.

The intermediate zone is able to exert a force substantially radiallytowards the inside against the axially outer portion of the bearingzone.

The arrangement of circumferential cords contributes to thecircumferential clamping force of the tire against the rim on which itis mounted. The level of clamping is determined so as to ensure a goodcompromise between the ease of mounting/demounting and the assurance ofreliable, durable mounting.

The intermediate zone ensures a mechanical connection between theanchoring zone and the bearing zone. The anchoring zone and theintermediate zone may be twinned mechanically. The same applies to theintermediate zone, which may be joined to the bearing zone. However, theanchoring zone is preferably not directly joined to the bearing zone.

The reinforcement structure of the sidewalls and the crown isadvantageously of the carcass type, its mechanical properties beingsimilar to those of carcass plies of known type. Furthermore, thisreinforcement structure is advantageously formed without axialseparation at the level of the bead. Thus all of the cords of thecircumferential arrangement preferably occupy a substantially identicalaxial position.

Preferably, the anchoring zone is radially external to the bearing zone.

The transfer of forces advantageously takes place by a moment of force.

The anchoring zone of the reinforcement structure in the bead isadvantageously formed at least in part of a rubber mix of substantiallyhigh modulus. This modulus may for example be substantially equal to orgreater than 20 MPa, and preferably greater than 40 MPa. The presence ofthis type of rubber mix contributes to the anchoring of the carcass-typereinforcement structure. The reinforcement structure is at leastpartially in contact with this mix, or even preferably at leastpartially embedded in the mix.

Preferably, the bearing zone is substantially elongated. It is extended,for example, substantially along the seat of the bead. The transfer offorces upon rotation of the bottom zone of the axially inner portion ofthe bead towards the axially outer portion of the bead is thus possible,while maintaining bearing pressure against at least a portion of theseat of the bead. The transfer of forces creates self-clamping of thetoe of the bead against the rim.

The bearing zone is preferably substantially adjacent to the rim seat.

Preferably, the anchoring zone is arranged in the portion of the beadwhich is substantially in the immediate vicinity of the carcass-typereinforcement structure. It may therefore be located either on only oneor on both sides of the reinforcement structure.

Preferably, the bearing zone is substantially formed of a rubber mix ofhigh modulus. The loading of this zone is thus limited and the contactwith the seat of the rim is optimized. The modulus may for example besubstantially equal to or greater than 20 MPa, and preferably greaterthan 40 MPa.

Preferably, the intermediate zone is substantially formed of a rubbermix of high modulus. It may advantageously be surrounded or encircled byone or more cords arranged around the zone, for example at 90°, so as toapply compressive stress to the zone. This modulus may for example besubstantially equal to or greater than 20 MPa, and preferably greaterthan 40 MPa.

According to another advantageous variant, the bead also comprises aloadable buffer zone, which is arranged in the radially inner andaxially outer portion and which is capable of bearing against a flangeof the rim. The presence of such a buffer zone promotes the rotation ofthe bottom zone and also makes it possible to secure the axial hookingof the bead against the rim flange. The presence of a zone of rubber ofhigh modulus in a radially inner portion relative to the flange providesgood axial holding and prevents the bead from sliding axially towardsthe outside.

According to another advantageous variant, the bead portions generallyaround the anchoring, intermediate and bearing zones are generallyoccupied by a material having an elasticity modulus which is lower thanthat of the material of the anchoring, intermediate and bearing zones.These various zones, in fact, have a certain relative mobility relativeto the rim seat on which the bead is mounted. This mobility is oftenexpressed by displacements of the angular or rotational type. Each ofthe zones also has a certain relative mobility relative to the adjacentportions of the bead, which are formed of rubber mixes of lower modulus,and/or relative to the other neighbouring zones. This mobility canexpressed, for example, by displacements of the angular or rotationaltype.

Preferably, the elasticity modulus of the rubber mix of high modulus isgreater than 20 MPa, and preferably greater than 40 MPa.

According to another advantageous example, the bearing zone and/or theintermediate zone is/are arranged and defined such that uponsubstantially axially external rotation of the bottom zone of the tire,none of the zones exerts a force against the rim flange or hook whichwould be liable to cause disassembly of the bead of the tire. Thus, forexample, the axially outer limit of the zones corresponds substantiallyto the outer limit of the rim on which the tire is likely to be mounted.

According to another advantageous variant, the intermediate zonecomprises a substantially radial arrangement of circumferential cords.Similarly, the bearing zone may comprise a substantially radialarrangement of circumferential cords.

Advantageously, the number of axially inner cords of the anchoring zoneis at most 1.5 times the number of axially outer cords. These are cordswhich are axially to the inside or the outside relative to thecarcass-type reinforcement structure.

Preferably, the bead of the tire comprises a carcass-type reinforcementstructure which extends substantially radially from each of the beads,along the sidewalls, towards the crown zone, each bead being reinforcedby a substantially radial arrangement of circumferential cords arrangedin stacks, a portion of the carcass-type reinforcement structure beingarranged in the immediate proximity of at least one portion of a stack,and the space between such portions generally being filled by a rubbermix of high elasticity modulus.

An interface zone is advantageously formed by a portion of thereinforcement structure and at least one stack, such zone beinggenerally embedded in a rubber mix of high modulus. Advantageously, theinterface zone generally covers the stacks and the adjacent portion ofreinforcement structure. Such an arrangement, in particular at the levelof the bead, permits very great flexibility in defining the variouszones comprising mixtures of different natures and/or characteristics.The same applies to the cords, which may be formed in a large number ofconfigurations. Taking into account these two aspects, it is possible tooptimize the design and manufacture of the tires, according to the typeof vehicle for which the tire is intended and the associated constraintsof use. It is also possible to provide more appropriate arrangementswhich facilitate certain types of automated manufacture, for examplewith assembly on a central core and/or without using semi-finishedproducts. It is thus possible to design a tire for a given vehicle whichcan be manufactured at lower cost.

The anchoring of the reinforcement structure in the bead is ensured,despite the absence of a bead wire of conventional type around which thecarcass is usually turned up to create a reliable anchoring link. Thistype of structure is also advantageous owing to its compactness, and iseasy to mount/demount. Furthermore, the traditional carcass upturn whichis found in beads of known types, comprising a seat having a generatrix,the axially inner end of which lies on a circle of a diameter greaterthan the diameter of the circle on which the axially outer end islocated, can be dispensed with without sacrificing the integrity,solidity or endurance of the assembly. This aspect contributes tosimplifying manufacture, while offering very great latitude in terms ofconfigurations.

Dispensing with the upturn is made possible by using mixes of highmodulus in the interface zone in direct contact with the carcass-typereinforcement structure in the anchoring zone. In the conventional tire,the carcasses are in intimate contact with mixes of low or very lowmodulus, which involves great lengths for transmitting the forces to thebead wire.

According to a particularly advantageous method of manufacture in whichthe various constituents of the tire are arranged directly on a centralcore, the shape of which imparts to the tire during manufacture asubstantially similar shape to the shape of the finished product,dispensing with the upturn (which exists with a conventional structure)permits advantageous simplification of manufacture.

Preferably, at least one outer flange of a bead is arranged so as to beextended substantially axially and radially towards the outside from theaxially outer end of the seat of the bead. For example, the outerflange, which is axially external to the seat, comprises a substantiallyrectilinear generatrix inclined radially externally relative to the axisof rotation of the tire by an angle of between 30° and 85°, measuredfrom such axis.

Such a flange is normally used together with a rim comprising a rimflange, commonly referred to as a “side”, also arranged so as to beextended substantially axially and radially towards the outside from theaxially outer end of the seat of the rim. This flange is capable ofserving as a bearing zone when the bead is subjected to a force whichtends to push it back radially towards the outside. This may be thecase, for example, when the phenomenon of rotation of the bead occursor, alternatively, under the influence of the stress induced duringsharp cornering. The flange contributes to holding the bead, and hencethe tire, on the rim properly, in particular avoiding any spilling-overaxially towards the outside.

According to an advantageous form of embodiment of the invention, thebases of the stacks (the cords radially closest to the axis of rotationof the tire) are arranged radially farther to the outside than the endof the rim flange (axially and radially outermost portion of theflange). The bases of the stacks are advantageously provided so as to bearranged radially externally relative to the flange of the rim which ismatched to the tire. The mounting/demounting operations are thenfacilitated.

Advantageously, the carcass-type reinforcement structure extendssubstantially radially from each of the beads, along the sidewalls,towards the crown zone. Such structure may thus be unitary and extendfrom one bead to the other, or alternatively may be divided into twohalf-structures, each extending along a single sidewall.

According to an advantageous variant, the substantially radialarrangement of circumferential cords is arranged in at least one stack,with each stack being arranged on the axially outer side relative to thecarcass-type structure.

According to another advantageous variant, the substantially radialarrangement of circumferential cords is arranged in at least one stack,with each stack being arranged on the axially inner side relative to thecarcass-type structure.

According to another advantageous variant, the substantially radialarrangement of circumferential cords is arranged in at least two stacks,the stacks being arranged on either side relative to the carcass-typestructure.

The number of stacks and the number of windings or turns of each of thestacks is advantageously established according to the characteristicsdesired for the tire, for example its operating pressure. For example, alarger number of stacks may be desired in order to increase the rigidityat the level of the zone of the bead.

The carcass-type structure is preferably formed of a cord windingextending back and forth between the two beads, forming loops in each ofthe beads. Furthermore, the cord winding is preferably formed of asingle cord.

According to an advantageous variant, the carcass-type structure formsan extension towards the axis of rotation of the tire beyond the base ofthe stacks. In such a case, since the upturn of the carcass-typestructure is not indispensable for anchoring purposes, the upturn may bemade without duplication with circumferential cords running along thestructure, and/or without the upturned portion being entirely orpartially arranged in a zone of rubber mix of high modulus.

According to another advantageous variant, the inner bead intended to bearranged on the inner side of the wheel and the outer bead intended tobe installed on the outer side of the wheel are arranged asymmetrically.Thus, for example, the number of stacks or the number of turns of eachof the stacks may be different. Some examples of asymmetricalarrangements are illustrated in the drawings, in which, for example, thenumber of stacks of cords in the bead on the inner side is differentfrom the number of stacks of cords in the bead on the outer side. Forexample, the number of stacks of cords in the bead on the inner side isless than the number of stacks of cords in the bead on the outer side.The reverse is also possible, depending on the desired characteristics.

According to another aspect, the symmetry relates to the arrangements ofthe anchoring, intermediate and bearing zones. Each of the beads mayhave different architectures in which, for example, the forms,arrangements and dimensions of one or more of the zones may vary. It isalso possible to vary the constituent materials, the mechanicalproperties, such as, for example, hardness, just as the number of zonescan be varied.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the invention will becomeapparent from the following description of exemplary embodiments of theinvention, which are given in non-limitative manner, with reference tothe accompanying drawings, in which:

FIG. 1 shows, in cross-section, a tire according to the invention;

FIG. 2 shows, in an enlarged cross-section, the beads of a first variantof a tire according to the invention, in which the stacks of cords arearranged on the same side of the reinforcement structure, namely, inthis example, the axially outer portion, and in which the three zones ofthe bead are twinned;

FIG. 3 shows, in an enlarged cross-section, another variant of beads, inwhich the different zones of the bead are arranged advantageously (thecircumferential cords are not shown in this figure);

FIG. 4 shows, in an enlarged cross-section, another variant of beads, inwhich the different zones of the bead are arranged advantageously (thecircumferential cords are not shown in this figure);

FIG. 5 shows, in an enlarged cross-section, another variant of beads, inwhich the different zones of the bead are arranged advantageously;

FIG. 6 shows, in an enlarged cross-section, another variant of beads, inwhich the different zones of the bead are arranged advantageously;

FIG. 7 graphically illustrates two curves which illustrate the rotationof the bottom zone of the tire according to the inflation pressure;

FIGS. 8 a to 8 e show the evolution of the position of a bead accordingto the invention on the rim intended for producing the assembly, as afunction of the inflation pressure;

FIG. 9 shows, in an enlarged cross-section, another variant of beads, inwhich the different zones of the bead are arranged advantageously;

FIG. 10 a shows, in cross-section, a tire according to the invention,mounted on a rim of suitable type; and

FIG. 10 b shows, in an enlarged cross-section, the tire of FIG. 10 amounted on a rim of suitable type.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

In the present description, the term “cord” very generally designatesboth monofilaments and multifilaments or assemblies such as cables,plied yarns or, alternatively, any equivalent type of assembly, whateverthe material and the treatment of the cords. They may, for example, besurface treatments, coating or pre-sizing in order to promote adhesionto the rubber.

The term “radial structure” is understood to mean an arrangement at 90°,but also, in accordance with custom, at an angle close to 90°.

It is known that, conventionally, the carcass ply or plies is/are turnedup about a bead wire. The bead wire then performs a function ofanchoring the carcass. In particular, it withstands the tension whichdevelops in the carcass cords, for example under the action of theinflation pressure. The arrangement described in the present applicationmakes it possible to ensure a similar anchoring role. It is also knownto use the bead wire of conventional type to ensure a function ofclamping the bead on a rim. The arrangement described in the presentapplication also makes it possible to ensure a similar clampingfunction.

In the present description, “bonding rubber” is understood to mean therubber mix which may possibly be in contact with the reinforcementcords, adhering to them and able to fill the gaps between adjacentcords.

“Contact” between a cord and a layer of bonding rubber is understood tomean the fact that at least part of the outer circumference of the cordis in intimate contact with the rubber mix constituting the bondingrubber.

“Sidewalls” refers to the portions of the tire, most frequently of lowflexural strength, located between the crown and the beads. “Sidewallmix” refers to the rubber mixes located axially to the outside relativeto the cords of the reinforcement structure of the carcass and to theirbonding rubber. These mixes usually have a low elasticity modulus.

The term “bead” refers to the portion of the tire radially internallyadjacent to the sidewall.

FIG. 1 shows, in cross-section, a tire 1 according to the invention.This tire comprises a first sidewall 5 adjacent to a first bead 3 whichpreferably corresponds to the axially inner bead. Similarly, theopposite portion of the tire comprises a second sidewall 6 adjacent to asecond bead 4. A crown 7, on which there is provided a tread 8, providesthe join between the sidewalls. The crown preferably comprises at leastone reinforcement belt.

The tire comprises a reinforcement structure 2, such as, for example, acarcass, provided with reinforcements which are advantageously shaped ina substantially radial arrangement. The structure 2 may be arrangedcontinuously from one bead to the other, passing via the sidewalls andthe crown, or alternatively it may comprise two or more parts, arrangedfor example along the sidewalls, without covering the entire crown.

The end portions of the reinforcement structure 2 cooperate with thebeads. There is thus effected anchoring of these portions in the beadsso as to ensure the integrity of the tire.

The reinforcement structure 2 can be formed by winding a single cordwhich extends back and forth between the two beads, forming loops ineach of the beads. These loops, which are coated in the rubber mix ofhigh modulus, contribute to the mechanical bond between thereinforcement structure 2 and the bead, in particular the stacks 13. Bythe presence of loops between the “back” and “forth” sections of thecord, it can be seen that the reinforcement is of the monofilament type.Of course, the carcass might not be manufactured continuously from asingle cord, and there might not be any loops, but rather, for example,cut ends.

As illustrated in FIG. 2, circumferential cords 12, preferably arrangedin the form of stacks 13, form an arrangement of cords 11, which isprovided in each of the beads 3 and 4. The cords 12 are preferably metalones. Part or all of the cords 12 may also be made of textile or othermaterials.

At least one cord 12 of one of the stacks 13 is preferably arranged inthe immediate proximity of an end portion 21 of the reinforcementstructure 2. The stacks 13 may also be arranged such that an end portion21 is inserted between stacks 13.

The space between the cords 12 and the reinforcement structure 2 isoccupied by a bonding rubber mix 14. It is also possible to provide forthe use of a plurality of mixes having different characteristics,defining a plurality of zones, the combinations of mixes and theresultant arrangements being virtually unlimited. However, it isadvantageous to provide for the presence of a rubber mix of highelasticity modulus in the zone of intersection between the arrangementof cords 11 and the reinforcement structure 2. By way of non-limitativeexample, the elasticity modulus of such a rubber may reach or evenexceed 40 MPa.

The arrangements of cords 11 may be arranged and manufactured in variousways. For example, a stack 13 may advantageously be formed of a singlecord 12, wound (substantially at zero degrees) in a spiral, preferablyfrom the smallest diameter towards the largest diameter. A stack mayalso be formed of a plurality of concentric cords laid one withinanother.

The position of the stacks 13 may vary in a virtually infinite number ofpossible ways. Some non-limitative examples are illustrated anddescribed in the present description. The base of the stacks (radiallyinner portion) may be substantially co-radial (aligned radially), asillustrated in FIG. 2, or be radially offset, for example such that allof the first cords of each stack form an alignment having a given anglerelative to the axis of rotation of the tire.

Surprisingly, it has been noted that anchoring of the reinforcementstructure in the bead can be effected by the type of interfacedescribed, despite the fact that in the tire of extended mobilityaccording to the invention, the forces induced at the bead differ fromthose of a bead of conventional type. For example, with the tireaccording to the invention, an increase in pressure causes an increasein the radial thrust of the seat of the bead against the seat of therim.

FIGS. 8 a to 8 e show the evolution of the angular position of thebottom zone of a tire, and in particular of the anchoring zone of a beadrelative to its initial geometry when not mounted and not inflated. Itwill be observed that the more the pressure increases, the more theaxially outer portion of the seat bears against the seat 20 of the rim.FIG. 8 a illustrates the non-inflated assembly, at zero bar. Thepositioning angle is then about 10°. FIG. 8 b illustrates the assemblyinflated to one bar. The positioning angle is then about 8°.

FIG. 8 c illustrates the assembly inflated to three bar. The positioningangle is then about 3°. FIG. 8 d illustrates the assembly inflated tosix bar. The positioning angle is then about −4°. FIG. 8 e illustratesthe assembly inflated to eight bar. The positioning angle is then about−11°.

FIG. 7 graphically illustrates two curves which illustrate the rotationof the bottom zone of the tire according to the inflation pressure. Thecurve A corresponds to an architecture in which the two stacks of cordsare arranged axially externally to the carcass-type reinforcementstructure 2. The curve B corresponds to an architecture in which two ofthe stacks of cords are arranged axially internally relative to thecarcass-type reinforcement structure 2. Curve A therefore corresponds toan example in which the reinforcement structure 2 is axially farthertowards the inside than in the example corresponding to curve B. Thelever-arm effect, for example relative to the center of pressure CP, isgreater in the first example.

It will furthermore be noted that the results of the rotation of thebottom zone differ in these two examples, such that an architecture inwhich the reinforcement structure 2 is axially farther towards theinside, and therefore with a larger lever arm, imparts more rotation tothe bottom zone of the tire, the other parameters such as thedimensions, constituents, etc., of course being similar in the twoexamples. Thus curve B of FIG. 7 has lesser rotation than curve A, forthe same variation in inflation pressure.

These tests have made it possible to note that it is possible tomodulate the level of rotation of the bottom zone of the tire by usingvarious types of architecture in which the relative positions of thecords 12 and/or of the reinforcement structure 2 vary relative to eachother or, alternatively, relative to a given point of the bead, such as,for example, the center of pressure CP.

By making a correlation between the graph of FIG. 7 and the variouspositions shown in FIG. 8, it will be noted that at zero or low pressurethe pressure is particularly concentrated on the axially inner portionof the seat; the more the pressure increases within the tire, the morethe stresses exerted on this portion axially to the inside of the seatdecrease and move towards a zone axially farther to the outside of thebead. From a certain value of the pressure of the tire onwards, theforces exerted in the two zones are equivalent; then the forces exertedin the zone axially to the outside can become larger than those exertedaxially to the inside. During this transfer, it is possible for thepressure exerted against the outer rim flange to increase as well.

Various tests carried out with different configurations have made itpossible to demonstrate the fact that this phenomenon of transfer of theforces, or, alternatively, rotation of the bottom zone, is due, on theone hand, to the increase in the pressure in the tire which creates aforce acting axially towards the outside and acting against the sidewalland the bead, and, on the other hand, to the increase in the tension inthe reinforcement structure following the increase in pressure in thetire.

FIGS. 3 to 6, and also FIG. 9, illustrate different examples ofarrangements of the zones of the bead. An anchoring zone 30, which isusually arranged axially to the inside, cooperates with the end portion21 of the reinforcement structure 2, so as to secure the structure 2 onthe bead. A rubber mix of high modulus contributes to creating thisanchoring. Beneath the zone 30, or more particularly in the radiallyinner portion of the bead, in the zone of the seat, a bearing zone 50 isprovided. The zone 50 acts as an interface between the rest of the beadand the seat of the rim. Major forces of the radial and axial type aretherefore transmitted by the zone 50. A rubber mix of high moduluscontributes to the transfer of these forces by ensuring good holding ofthe bead against the rim.

Between these first two zones 30, 50, an intermediate zone 40 isprovided, so as to ensure mechanical continuity. The forces can thus betransmitted from the anchoring zone 30 towards the bearing zone 50, viathe intermediate zone 40.

FIG. 3 shows an arrangement of the three zones such that the zones 30and 40 are substantially radially side by side, with the zone 50 beingarranged radially to the inside of the other two zones. The zone 50 isseparated from the other two zones 30, 40 by a substantially axial,rectilinear inter-zone space. An inter-zone space is present betweeneach of the three zones. According to various variants which have notbeen shown, the zones are joined two by two, for example the zone 30 istwinned with the zone 40, the zone 40 is twinned with the zone 50, etc.Such zones are then no longer separated as in the example of FIG. 3.

The three zones may also be joined, to form a unified assembly such asillustrated, for example, in FIG. 2.

The inter-zone spaces are advantageously occupied by a rubber mix of amodulus which is lower than that of the mixes forming the zones.

FIG. 4 shows an example similar to that of FIG. 3, except that the zone50 extends radially internally as far as the edge of the bead or as faras the seat. For clarity of the illustration of the zones, thecircumferential cords 12 of the anchoring zone 30 are not shown in FIGS.3 and 4.

FIG. 5 shows another example similar to that of FIG. 3, with the zone 50extending radially and axially outwards so as to form a V-shapedinterface with the other two zones.

FIG. 6 shows an example similar to that of FIG. 3, also comprisingalignments or stacks of cords 12 in the intermediate zone 40 and/or inthe bearing zone 50. These cords serve in particular to clamp the beadon the rim. They may be cords of the metallic, hybrid or textile type.

The tire according to the invention is particularly suitable for use ona rim of the type described in EP 0 673 324 (U.S. Pat. No. 5,634,993,the disclosure of which is hereby incorporated by reference). Such a rimcomprises a seat and preferably a raised area or flange located axiallyand radially towards the outside. The quality of the contact or of thebearing of the bead on the seat is particularly important. One of themeans according to the invention used to improve such contact or bearingconsists in optimizing the phenomenon previously described of rotationof the bottom zone of the bead.

This phenomenon arises from the structure of the bead used. The axialposition of the reinforcement structure 2 relative to the center ofthrust CP of the bead may to a certain extent influence the moment Mcreated by a tensile force T induced in the reinforcement structure 2.This moment M acts on the rotation effect of the bottom zone of thebead. See FIG. 2.

Owing to the phenomenon of rotation of the bottom zone of the bead, thebead, in particular at the level of the seats, bears more on thecorresponding bearing face of the rim, which makes it possible toincrease the cohesion at the level of the rim/tire interface. Thisaspect is particularly important, for example when a vehicle roundstight curves or, alternatively, corners at high speed. Thesecharacteristics therefore contribute to improving the safety of thetire/rim assembly and hence of the vehicle.

Among other things, the choice of one or the other of the variantsillustrated in the various figures makes it possible to influence thephenomenon of rotation of the bottom zone of the beads.

These figures illustrate several examples of arrangement of thereinforcement structure 2 relative to the stacks 13 of cords. Thus, inFIG. 2, the stacks of cords are arranged on the same side of thereinforcement structure 2; in this example, the axially outer portion.

FIG. 5 shows a variant in which the reinforcement structure 2 isinserted between a stack 13 of cords 12 arranged axially to the insideand a stack 13 of cords 12 arranged axially to the outside relative tothe structure 2.

FIG. 9 shows another variant in which the stacks 13 of cords arearranged on the same side of the reinforcement structure 2; in thisexample, the axially inner portion.

These examples are given merely by way of illustration: other variantswith, for example, more or less stacks 13 possibly comprising differentnumbers of cords 12 may be used.

These different variants of embodiments provide different mechanicaleffects at the level of the beads, the anchoring of the reinforcementstructure and, consequently, at the level of the rim/tire interface.Thus, with a variant of the type shown in FIG. 2, the lever arm betweenthe structure 2 and the center of thrust CP is large, providing a largemoment M. On the contrary, in a variant of the type shown in FIG. 9, thelever arm is rather short, which limits the value of the moment M. Thelatter will therefore have a lower value in the second case than in thefirst.

The geometry or the arrangement of the bonding rubber 14 may alsoinfluence the phenomenon of rotation of the bottom zone. FIGS. 2 and 6illustrate this fact. Given the probable presence of a protrusion orflange on the rim, which is capable of bearing against the outer bearingzone of the bead, the rotation of the bottom zone will involve areaction force R coming from this protrusion. To facilitate the rotationor to enable it to be greater, it is preferable to limit the reactionforce R. In order to do this, a buffer zone is provided on the beadbetween the zone of mix of high modulus and the flange of the rim.

The buffer, or loading, zone 17 is formed of a material which is moreflexible than that generally located in the interface zone between thearrangement 11 of cords and the reinforcement structure 2. As describedpreviously, under the combined action of the pressure of the tire and atension T acting on the structure 2, the moment M thus created acts toload the zone 17, thus promoting the rotation of the bottom zone of thebead.

The zone of loading 17 is preferably located along the outer axialprofile of the bead provided to be arranged adjacent to the rim flange.For example, the zone 17 may be located, as illustrated in FIG. 6,between the radially outer portion substantially adjacent to theradially lower point of the bead, and extended axially and radiallytowards the outside, so as to form the outer contour of that portion ofthe bead which is able to run along the rim flange.

The bases of the stacks 13 (the cords radially closest to the axis ofrotation of the tire) are preferably arranged radially farther to theoutside than the end of the flange (axially and radially outermostportion of the flange), as illustrated, for example, in FIG. 6 and inFIGS. 10 a and 10 b. The bases of the stacks are advantageously providedso as to be arranged radially externally relative to the flange of therim 60 which is matched to the tire. The mounting/demounting operationsare then facilitated. Thus, in FIG. 6 and FIG. 10 b, it will be seenthat r_(f) (radius of the first cords) is greater than r_(j) (radius ofthe rim flange or hook). This radius corresponds to the distance orspacing from the axis of rotation.

The elasticity modulus of the mix used in the loading 17 zone may, forexample, be between 10 and 40 MPa, but is preferably less than 20 MPa.“Elasticity modulus” of a rubber mix is understood to mean a secantmodulus of extension obtained at a uniaxial deformation of extension ofthe order of 10% at ambient temperature.

The interface zone between the reinforcement structure 2 and thearrangement of cords 11 may be provided such that the reinforcementstructure 2 is interposed between or close to the stacks 13, with theend portion 21 of the structure 2 being located in a given radialposition somewhere along one of the stacks, or alternatively close tothe base of a stack, but without significantly extending beyond the baseof the stacks in the direction of the axis of rotation of the tire.

Otherwise, according to another aspect of the invention, the end portion21 may be located radially closer to the axis of rotation of the tirethan the base of the stacks 13, thus creating an extension 15 of thereinforcement structure 2 beyond the base of the stacks 13. FIG. 2 showsan example of such an extension 15. The extension 15 may then take alarge number of arrangements, such as, for example, an alignmentsubstantially parallel to the seat 10, an alignment substantiallyparallel to the axis of rotation of the tire, etc.

According to another variant, the end portion 21 forms an upturn aroundthe stack or towards the axially outer stack or alternatively betweentwo stacks, preferably stacks other than those via which the structure 2enters the bead.

The length of the extension 15 may vary from a few millimetres to a fewcentimetres.

FIGS. 1 and 2 illustrate another aspect of the invention, according towhich the stacks 13 of cords 12 are arranged asymmetrically in the twobeads. This type of arrangement is particularly advantageous for a tirecomprising beads which are not identical, either because of theirshapes, their profiles, their dimensions, their constituent materials,their average distance from the axis of rotation of the tire, etc.

Document EP 0 673 324 (U.S. Pat. No. 5,634,993) illustrates an exampleof such a tire. In fact, since it is used on a rim comprising anon-symmetrical profile and the profile of the beads is matched to thisprofile, the bead profile is asymmetrical.

Furthermore, owing to the position of the tire on a vehicle, the twobeads do not have to be subjected to the same levels of forces andstresses. Frequently, the bead on the outer side of the tire is moregreatly stressed. It is therefore preferable to optimize the arrangementthereof so that it can withstand high levels of stresses. Since theaxially inner bead 3 generally does not have to be subjected to suchhigh levels of stresses, its structure can be simplified.

In the example of embodiment illustrated in FIG. 1, the first bead 3comprises three stacks 13 of cords, while the second bead 4 comprisesfour. The production of the first bead therefore requires less materialand fewer manufacturing steps. This type of architecture is thereforemore economical.

In order to make allowance for a maximum number of physical andmechanical stresses, not only the number of stacks of cords, but alsothe number of cords per stack, the arrangement of the types of rubbersbetween them, the shape of the bead, the number of zones (anchoring,intermediate, bearing), their forms, their dimensions, the nature or thematerial of the cords, etc., may vary from one bead to the other.

Not only is it possible, therefore, to contribute to reducing the costsof the finished product, but it is also possible to optimize thestructures of each of the beads 3 and 4 according to their respectivespecific features, which is not possible on a symmetrical profile. Inthis latter case, the single arrangement applied to both beads is formost of the time a compromise taking into consideration, as far aspossible, the sometimes contradictory properties desired for each of thebeads.

The different examples of embodiment described and/or illustrated mayadvantageously be produced using devices of the types described in EP 0580 055 (U.S. Pat. No. 5,616,209).

Thus, for example, it is very advantageous to build the tire on acentral core which imposes the shape of its internal cavity. There areapplied to this core, preferably in the order required by the finalarchitecture, all the constituents of the tire, which are arrangeddirectly in their final position, in a substantially final profile. Inthis case, such a tire can be moulded and vulcanised as set forth inU.S. Pat. No. 4,895,692.

1. A tire for a vehicle wheel, comprising: two sidewalls spaced apartaxially from each other and joined at their radially outer portions by acrown zone provided on its radially outer portion with a circumferentialtread; a bead, arranged radially to the inside of each of the sidewalls,each bead comprising a seat and an outer flange which are intended tocome into contact with a suitable rim; a reinforcement structureextending substantially radially from each of the beads, along thesidewalls, towards the crown zone; at least one of said beadscomprising: (1) a bead seat comprising a generatrix, the axially innerend of which lies on a circle of a diameter greater than the diameter ofthe circle on which the axially outer end is located; (2) an anchoringzone for the reinforcement structure in said bead, comprising asubstantially radial arrangement of circumferential cords arranged inthe vinicity of a portion of said reinforcement structure and comprisingat least two cords distributed on each side of said reinforcementstructure, and an anchoring rubber mix being disposed between saidcircumferential cords and said reinforcement structure; (3) anintermediate zone, arranged substantially axially externally to theanchoring zone and comprising at least one portion substantiallyradially aligned with said anchoring zone; and (4) a bearing zone forsaid bead which is able to lie directly or indirectly against thesuitable rim seat, and comprising at least one portion axially alignedwith said intermediate zone and placed radially internally with respectto said intermediate zone.
 2. The tire of claim 1, in which saidintermediate zone cooperates, on the one hand, with said anchoring zoneand, on the other hand, with said bearing zone, so as to provide amechanical connection between said anchoring zone and said bearing zone.3. The tire of claim 1, in which said intermediate zone permits thetransfer of forces from the anchoring zone to the bearing zone of thebead.
 4. The tire of claim 3, in which the transfer of forces takesplace by a moment of force.
 5. The tire of claim 1, in which saidbearing zone is substantially elongated.
 6. The tire of claim 1, inwhich said bearing zone is substantially adjacent to the rim seat. 7.The tire of claim 1, in which said bearing zone is substantially formedof a rubber mix of high modulus.
 8. The tire of claim 1, in which saidintermediate zone is substantially formed of a rubber mix of highmodulus.
 9. The tire of claim 1, in which said bead also comprises aloadable buffer zone which is arranged in the radially inner and axiallyouter portion thereof, said buffer zone being capable of bearing againsta flange of the rim.
 10. The tire of claim 1, in which the bead portionsgenerally around said anchoring, intermediate and bearing zones aregenerally occupied by a material of an elasticity modulus lower thanthat of the material of said anchoring, intermediate and bearing zones.11. The tire of claim 8, in which the elasticity modulus of said rubbermix of high modulus is greater than 20 MPa, and preferably greater than40 MPa.
 12. The tire of claim 1, in which the axially outer limit ofsaid zones corresponds substantially to the outer limit of the rim onwhich the tire is likely to be mounted.
 13. The tire of claim 1, inwhich the intermediate zone comprises a substantially radial arrangementof circumferential cords.